Place the CppUnit:assertion_traits for ::table::CellAddress and
::table::CellRangeAddress into a file, so that they can be used/shared
from several locations. Avoid copy/paste action.

Change-Id: Ie2358ea1ac6925eef05644bea03a2ae526cd7fc6
Reviewed-on: https://gerrit.libreoffice.org/44291Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jens Carl <j.carl43@gmx.de>